H. An electrical signal travel down the dendrite.

Transcription

1 Nervous System Group Activity Objectives: To be able to describe the nervous system structure and function To understand how neurons communicate using both electrical and chemical signals To know how the nervous system controls and responds to body functions and directs our behavior Place the following steps in the order that they occur in the signaling cascade on the next page. You may answer using the letters associated with each action. Use the diagrams provided to guide your answers. A. Voltage- gated Na + channels inactivate and voltage- gated K + channels open. K + exits the cell to repolarize the cell membrane, while Na + diffuses further down the axon, depolarizing the membrane towards the nearest Node of Ranvier. B. Interneurons communicate with motor (efferent) neurons to send a signal away from the central nervous system. C. Voltage- gated Ca 2+ channels open. Ca 2+ moves across the cell membrane and into the cytosol. D. The axon receives an electrical signal from the axon hillock. E. Intracellular Ca 2+ binds to vesicles and triggers the release of neurotransmitters into the synaptic cleft via exocytosis. F. Neurotransmitter molecules are removed from the synaptic cleft. They are either taken up by the presynaptic cell or are degraded by enzymes. G. Previously inactivated Na + channels close completely, but continued K + diffusion results in hyperpolarization of the membrane and a brief refractory period before returning to resting potential. Na + channels further down the axon open in order to conduct the action potential H. An electrical signal travel down the dendrite. I. Neurotransmitters open ion channels in the postsynaptic cell, causing the cell membrane to depolarize and an excitatory postsynaptic potential (EPSP) is produced in the next nerve cell.

2 1 A stimulus is detected by a sensory (afferent) neuron 2 3 The cell body processes the signal and produces an outgoing signal 4 5 An action potential is triggered, causing voltage- gated Na + channels to open. Na + diffuses into the cell and depolarizes the cell membrane Voltage- gated K + channels sequentially close and resting membrane potential is restored The action potential moves quickly down the axon in a saltatory motion until it reaches the axon terminal Neurotransmitters diffuse across the synaptic cleft and bind to receptors embedded in the postsynaptic cell membrane The signal reaches interneurons in the central nervous system, which interpret the information 17 A response is generated, such as movement or the secretion of hormones from endocrine glands.

3 Read the descriptions of the following conditions below. For each condition, determine which step in the signaling cascade is disrupted. Then, use what you know to choose the reason why this step cannot be completed correctly. A. Tetrodotoxin (abbreviated TTX) is a potent neurotoxin found in a pufferfish that is often served in sushi restaurants as a delicacy. However, when improperly prepared, this dish can result in poisoning. Ingestion of TTX first causes numbness of the lips and tongue, followed by increasing paralysis. When ingested in larger amounts, full loss of movement occurs, followed by death. Below is a diagram of a series of action potentials of a normal person (Control) and a person suffering from TTX poisoning (TTX). Tetrodotoxin poisoning disrupts which of the following steps? a) Voltage- gated Na + channels open and Na + diffuses into the cell to depolarize the membrane b) K + diffusion causes hyperpolarization of the membrane, resulting in a brief refractory period before returning to resting potential c) Voltage- gated Ca 2+ channels open so that Ca 2+ moves across the cell membrane and into the cytosol d) Neurotransmitter molecules are removed from the synaptic cleft This step cannot be competed because TTX: a) increases the threshold level required for an action potential b) blocks Na + channels c) binds to the neurotransmitter receptors d) blocks K + channels

4 B. Major depressive disorder is a neurological condition that results from abnormal neuronal activity within the area of the brain involved in processing emotion. Drugs can be prescribed to individuals suffering from this disorder. Commonly, selective serotonin reuptake inhibitors (SSRIs) are effective at reducing or removing the symptoms of depression. SSRIs function to increase the extracellular concentration of serotonin by blocking neurotransmitter reabsorption, as seen in the figure below. Major depressive disorder disrupts which of the following steps? a) Intracellular Ca 2+ binds to vesicles and triggers the release of neurotransmitters into the synaptic cleft via exocytosis b) Neurotransmitters diffuse across the synaptic cleft and bind to receptors embedded in the postsynaptic cell membrane c) Interneurons send a signal away from the central nervous system d) A response is generated, such as movement or the secretion of hormones This step cannot be competed because people suffering from major depressive disorder: a) have very low levels of cytosolic Ca 2+ b) have mutant neurotransmitter receptors in the post- synaptic cell c) have low levels of the neurotransmitter serotonin d) are incapable of synthesizing any neurotransmitters

5 C. Multiple sclerosis is a serious autoimmune disease that affects the transduction of nervous signals. Symptoms of this disease often include loss of sensitivity, difficulty moving, problems speaking, and a loss of coordination and balance. Further, people diagnosed with this disease (open circles) take longer to respond five different stimuli than do healthy individuals (closed circles), as diagrammed in the graph below. STIMULUS TYPE Multiple sclerosis disrupts which of the following steps? a) An electrical signal travels down the dendrite b) An action potential is triggered, causing voltage- gated Na+ channels open membrane depolarization c) The action potential moves quickly down the axon in a saltatory motion d) Neurotransmitters diffuse across the synaptic cleft and bind to receptors embedded in the postsynaptic cell membrane. This step cannot be competed because multiple sclerosis: a) degrades the myelin sheath surrounding nerve cells b) causes in fewer ion channels to open c) reduces the number of interneurons available to communicate with motor neurons d) results in neurotransmitters that cannot bind as tightly to receptors in the post- synaptic cell